The present invention relates generally to seals and particularly to fabric seals for usage in low leakage static or dynamic sealing applications.
The increased worldwide demand for electricity leads to the necessity of designing large-scale, high-powered, high-efficiency, and low cost power generation turbomachines with high standards for reliability and performance. One of the primary concerns in a turbomachine design is its sealing performance because it has direct impact on machine operating reliability and efficiency. A number of seals are used in turbomachines such as gas/steam turbines, compressors, and generators for minimizing leakage flows. According to the movement of a seal relative to its sealing surface, seals can be classified as stationary seals affording leakage barriers around and between stationary components or rotating seals affording leakage barriers between stationary and rotating components. Over the years, various techniques have been developed to improve both stationary and rotating seals. Much of this development has occurred in the turbine industry where parasitic flow control is critical.
As a circumferential contacting seal, brush seals have been widely used in turbomachines due to their distinguishing characteristics, i.e., lower leakage flow rate compared with labyrinth seals and seal flexibility for accommodating excursions at the interface without excessive wear and loss of sealing capability. However, brush seals formed of brush bristles are usually expensive and have exhibited hysterisis and were difficult to manufacture. The crucial seal parameters such as cant angle and bristle height depend on the process capability or manufacturing technique and are very difficult to control. A conventional brush seal is made by either folding bristles over a metal plate or sandwiching bristles between a pair of ring-shaped metal support plates and welding ends of the bristles and plates to one another adjacent common edges thereof. Since the metal bristle holder is usually machined with a tight tolerance, a brush seal can fit only a specific sealing dimension. This can result in very high costs for brush seals in tooling, manufacturing, and installation and leads to a long cycle time in brush seal fabrication.